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PET bottle production process-blowing bottle

Carrie Jul 24,2019 Share this post:

The whole process of blowing the PET bottle in the process can be divided into four stages: stretching, pre-blowing, blow molding and cooling.

When the temperature adjustment process is completed, the mold is closed, the stretching rod is moved downward, and the preform is stretched downward along the axial direction. The speed at which the stretching rod descends is controlled by the stretching cam. The material distribution of the PET bottle along the axial direction is formed at this moment. The stretching speed is one of the key parameters affecting the distribution of the material in the axial direction. If it is too fast, the material at the bottom of the bottle is too much, resulting in the distribution of the material on the body of the bottle. Insufficient, overall mechanical performance is reduced. Of course it is too slow. If the material at the bottom of the bottle is too small, the overall mechanical properties will be degraded and the ideal bottle will not be blown.

The function of the pre-blowing is to ensure that the preform material and the tensioning rod are always kept at a certain distance during the stretching process, and the contact between the preform wall and the stretching rod is avoided. During the stretching process, if the preform is in contact with the material and the stretching rod, the material is cooled by the stretching rod, and the friction between the stretching rod and the adhesion of the hot PET material causes the contacted portion. Unable to stretch as expected and unable to blow a qualified bottle. So the pre-blowing process is very important. Pre-blowing pressure and time settings are critical. The pre-blowing pressure is generally adjusted to about 6~10 bar. If the pre-blowing is not enough, the purpose of separating the stretching rod from the bottle wall material is not achieved. If the pre-blowing is excessive, the bottle wall material is not fully stretched. In good cases, the inner wall of the mold is touched in advance, which also affects the distribution of the material in the height direction and does not reach the expected material distribution.

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